The massive water is pushing a massive amount of debris along with it, according to the New Orleans Times Picayune. It's not just trees or cars or building debris: a Louisiana environmental group worries about leaks in treatment tanks for oil refineries and chemical plants. The Louisiana Bucket Brigade fears toxic material could flow into residential areas, now abandoned as floodwaters threaten people in the low-lying river basin.
NPR's Greg Allen is in Louisiana, where he stood atop the Morganza spillway when it opened and watched flooding surge into pastureland. He says even with the flood gates opened, there's so much water pressing against other levees along the river that crews are on the lookout for "sand boils". These occur when muddy water bubbles up through an earthen dam, suggesting some of the material may be giving way to the powerful water.